Well I ran the bike through my new test section just to see what kind of speed I'd have at the end. A 5th gear punch from 50 kph which netted 90 kph at the finish-a nice rpm range to test mods in perhaps.

Then...I rode around a bit, eventually pulling out of a local subd and hit it..WOW banging the 1-2 shift I got a big long power wheelie, 2-3 shift-another wheelie! I don't know if it's the 125 main jet, the timing or what, but this little 34mm carb/timing combo is making some nice power!

I hadn't banged any gears the other day, I just went for a sort of easy test ride other than letting it rev in 1,2 & 3 to see if it'd hit the rev limiter. So this was the first 1st gear punch accel test from slow roll since the timing mod.

I'd say it's quicker than back when I was riding it with the 34 all the time, but on the other hand my a/f tests showed I'd been too rich back then. Which has been 'fixed'. I'd bet on the timing change?


So now I wonder how it'd react with one of the bigger carbs

I may have to invest in a Veypor and hope to sell it when I am done

 

It isn't the power, it is the response. That is exactly what the VIP does, make the carburetor act as a smaller venturi in the early throttle opening. Too big a venturi will cause a stumble. What works well on general street use of any sort may not compare to the small throttle opening demands of off roading. That is evident in the example I gave - trials vs enduro vs motocross.

That is also what TNC is getting at, the demands of working one's way through a rocky tough trail or muddy slippery roots and ruts demands top level actions at smaller throttle openings. The opposite occurs a bit too much with the CV - the slide doesn't react fast or possibly predictably enough for the rider's need. Big carbs with quick opening tend to "gulp" and possibly stall, but either way that ever so brief hesitation in action may be the problem in a tough spot on a trail.

Similar experience was riding the early four stroke trials bikes versus the two strokes. When one needed to wheelie over an obstacle with the two stroke one just cracked it open and gave a light tug. With the four strokes one had to crack the throttle, make a light hesitation, then the light tug. The two stroke reacted near immediately the four stroke has a brief hesitation due to the firing order (every rotation of the crank vs every other).

Back to the timing thing. This is one where a Dremel could slot the holes and do the work. One where I wish I had the time and money to try it. A heated garage would help...


Side note on two strokes and definitely the trials bike - the Sherpa T and Metralla both could, and a few times - did kick back on starting, firing up and running backward as a "coil, points and plug" ignition could do. One guy didn't believe my friend and former owner of the Metralla until one day when he said "watch this!" and backed out of his parking place. Timing was close enough for it to run either way.

 

Nice, but theory time on the 40mm is over. It's been tried and the results are in You can use results to debate theory, but you can't use theory to debate results. If it hadn't been tried yet, then you could debate it forever; but I've been riding it and there isn't anything about the 40 that's an obvious drawback. It doesn't fall on its face, and it doesn't go from 2-14hp with a minor twist of the wrist.

You both seem to be pressing the "big carb-no good" thing as if I wasn't familiar with the premise at all. There's no stumbling or hesitation or anything negative associated with using the 40mm carb. If you can get through a technical section with the 36mm, then 99.9% of the time you'll do just as well with the 40. You could go on the same way about an exhaust system that added power up top, but you'd be zeroing in on the 1% chance it'd not be as good as what you have now. - Which you could do about most any mod.

Unfortunately the 40 hasn't shown itself to be quicker yet than the 36 at 250cc. Maybe after I do the cam mod? Which really seems to be the next mod to do before I test the other little things. Or maybe not until I install the 331.


Buy one of those brackets that holds the pick up coil for $3 plus shipping and see if it can sliced, moved 3mm, then rewelded. You can do that inside where it's warm

 

No Richard, they (TNC, KLX678) are right - the world is flat and your experiments won't change that. Maybe I could start a "What oil is best" thread to distract them all.

 

I did the bracket mod to my CBR125 land speed bike, but it wasn't enough. Any word on the FW diameter?

 

I missed the part where you were climbing a greasy up hill or picking your way up hill on a rocky trail working just above idle to half throttle to keep it on the line. Acceleration and top speed runs are fine and dandy, but do NOT tell the whole tale. This is what TNC and I point out. You are aiming for territory that is peachy on the street, but no actual evidence that it is just as good in tough off roading. That 1% is the difference between making for a nice ride dealing with the tough terrain and being miserable trying to work the clutch and rev the snot out of the bike to try to keep going. Only a small portion of the trail riding may be really difficult and complex, but it can be a make or break situation when it comes to enjoyable riding.

You are right about the faults of other modifications too. Cam changes are prime example. Most will start, run, and pull from idle, but not all are equal. I have a mild dirt cam in my SR500, there is a full race cam for roadracing and flat track, but not too good for short tracking or playing about on the road. Same can happen with headers too.

As long as it's all about peak speed and riding that favors sheer horsepower the big carbs, cams and such may come out good, but when it's put in the woods on tough single track the story changes and that's what some of us run. One reason the Marcelino mod was so attractive - more power over most of the range, pulling stronger down low, not pushing the good power delivery up high.

As for the 40 you proved it can be put on the bike and run, but not shown any gain over the 36, glad you did it, now I know not to do it. It's really good of you to do all the stuff you do so others can do like I have in other cases - learn from others' experience. I took a chance a number of years back putting a Vulcan piston in my KLX650 for a big bore. A fair number have been done since then in the KLX650 world, but I took the chance that it would work. Did the measurements to verify how close it was and did it. Another rider there did the DRz400 shock fitting and instructions on it for others to do the job. I was one of the early riders to do the cam chain tensioner with the 650 too, after ruining cam chains. Made a few extra and the guys snapped them up at half the cost of anything similar and it's led a lot of ways since.

By the way I will tell you a fair amount of my garage time is dedicated to what I do to help others keep their bikes going, not working with my own motorcycles, so there are contributing factors to lack of time to do some things. Not everyone is in the same situation you are. It may take a week for me to pull the carb, jet it and get it back on the bike, others might have a tougher time doing so due to family commitment. It doesn't make us any less than you.

 

Richard, I would very much like to know the "end of the story" on the modded ignition trigger on that stock flywheel with the CVk, Or any other carb.... Are you going to do a back to back - before and after comparo of the ignition mod ?

 

I'm thinking we've had "a few weeks" experience in and around IC engines and knowing what has transpired in the past makes us understand Albert Einstein's famous quote about doing the same thing over and over, expecting different results.

When the best tuners in the world are not pursuing a very easy avenue of experimentation for horsepower there is a reason - they tried it already and didn't get results. I have to believe Troy Lee and Mitch Peyton, along with Rob Muzzy and others had tried bolting on and jetting in a bigger carburetor on their 250s and 450s. They'd be fools to not have done so. Had they worked, it would be well known what to do. Kits would be sold. They are not.

It's hard to dispute what the best tuners in the world are doing when it comes to a $500 carburetor. It's also hard to dispute what the manufacturers, who want to beat each other, are installing on their motocross bikes. Are they flat earth too?

 

Thanks klx678, inspirational as always.. So how bout it Richard, what's the plan for your two flywheels?

 

I just dropped off the 1/2 pound lighter flywheel to have 3mm added to its nose. It'll be done in a couple days. After that and after maybe the MCM, I can try figure out how if at all to compare the two, but it'll be a lightened vs stock weight flywheel-they'll both have advanced timing.

I've contacted the Veypor people to see about sending one here. Not sure if I'll actually buy one because there isn't that much to test overall.